Doco-CD versions before 0.90.1 have a trust-boundary flaw in OCI artifact signature verification. When global OCI signature verification is enabled, an attacker with write permissions to the OCI tag can publish an artifact with a `.doco-cd.yml` file that sets `oci.verify: false`, effectively bypassing signature verification. This occurs because the deployment config inside the artifact influences the verification policy, allowing downgrade attacks. The fix in version 0.90.1 treats artifact-contained deployment configs as untrusted for trust-policy decisions and disallows disabling verification per deployment if global verification is enabled. Workarounds include avoiding sourcing deployment config from untrusted artifacts, restricting write permissions, using immutable digest pinning, and monitoring for suspicious verification events.

An attacker with write access to the OCI repository/tag can bypass cryptographic signature verification, causing untrusted deployment content to be applied. This can lead to integrity violations and potentially impact the integrity and availability of deployed services. The vulnerability does not affect confidentiality but can cause integrity and availability impacts as per the CVSS vector.

A fix is available in doco-cd version 0.90.1 that enforces strict trust boundaries and disallows disabling verification per deployment when global verification is enabled. Users should upgrade to version 0.90.1 or later. Until then, users should avoid sourcing deployment config from untrusted OCI artifact contents, use trusted inline deployment overrides, restrict write/push permissions on OCI repositories/tags, prefer immutable digest pinning, and monitor for unexpected artifact changes and verification failures.